2010 mustang Gt

starter relay perhaps

It’s possible your anitheft has kick on

I recently had the same problem. I bought a 2010 Mustang from a used car dealership about 7 weeks ago. All is fine until about three weeks ago when the car wouldn’t start. I went on YouTube and tried what other people suggested. (Turn key in on position for ten minutes to reset alarm,,,turn key on and off quickly for a minute, etc. nothing worked) The issue was Ford Motor company PATS system (factory alarm). The first time it wouldn’t start I brought it to local mechanic and after much diagnostic it was determined that it was the Transceiver. So paid to get a new one. Two days later 2010 mustang wouldn’t start. Had it towed to another mechanic. After two days he said the PATS was locking out car. I then had it towed to Ford dealership. They ran a bunch of test and apparently previous owner fucked with the security system PATS wiring to install a remote starter. I had to dish out almost $600 bucks to get the security system wired back and to have the half dozen codes cleared. The PATS system is build in the vehicle and you cannot take it out. Also, only a Ford dealership has the proper computers and codes to clear system. I tried to save a few bucks by going to local mechanics. My advice, go to a certified Ford dealership. Good luck